controls perception and experience of the world, directs voluntary movement, seat of consciousness, personality, learning, and memory, regulates aspects of homeostasis with the endocrine system (respiratory rate, blood pressure, body temp, etc.)
divided anatomically into central nervous system (CNS) and peripheral nervous system (PNS)
brain and spinal cord
cranial nerves, spinal nerves and their branches
Sensory, Integrative, Motor
gathers information about internal and external environments: somatic, visceral
carry signals from skeletal muscles, bones, joints, and skin, also from organs of vision, hearing, taste, smell, and balance
transmit signals from viscera (heart, lungs, stomach, kidneys, and urinary bladder)
analyze and interpret incoming sensory information: determine an appropriate response, 99% of integrated sensory information is subconsciously disregarded as unimportant, remaining sensory stimuli that CNS does respond to leads to motor response
actions performed in response to integration by motor (efferent) division of PNS: subdivisions into somatic and autonomic divisions by organs that neurons contact
neurons transmit signals to skeletal muscle: voluntary control
neurons carry signals to thoracic and abdominal viscera critical for maintaining homeostasis
excitable cells responsible for sending and receiving signals as action potentials, most consist of 3 parts
dendrites and cell body
axon
axon terminal
most metabolically active region, manufactures all proteins needed for whole neuron
both free ribosomes and rough endoplasmic reticulum (protein synthesis)
vesicular transport
supply energy required in the cell body
microtubules, structural support and chemical transportation between cell body and axon
intermediate filaments extending into neuron processes
short, branched processes: receive input from other neurons, which they transmit toward the cell body as electrical impulses: each neuron may have multiple dendrites
the ability of cells to transmit electrical impulses
local potentials, action potentials
travel short distances
travel entire length of axon
thin layer of negativity charged ions exists in cytosol on inside of cell, thin layer of positively charged ions exist on outside of cell, typical neuron has resting membrane potential (RMP) at -70mV
electrical gradient established by separation of charges between two locations (across plasma membrane)
electrical potential across cell membrane, source of potential energy for cell
cell is polarized when voltage difference across plasma membrane does not equal 0mV
ions cannot diffuse through components of the plasma membrane, and must rely on specific protein channels
always open, continuously allow ions to flow down concentration gradients between cytosol and ECF
closed at rest, open in response to specific stimulus
open in response to binding of specific chemical (ligand) to a specific receptor
open in response to changes in voltage across membrane
open or close in response to mechanical stimulation (pressure, stretch, or vibration)
most important ATP-consuming pumps, moves 3 sodium ions out and 2 potassium ions into cells per ATP hydrolyzed, maintains a high concentration of sodium in extracellular fluid and lower concentration in cytosol: opposite true for potassium
when cell returns to resting membrane potential
small local changes in potential of neuron's plasma membrane, triggers for long-distance action potentials, may cause one of two effects
positive charges enter cytosol, make membrane potential less negative (change from -70 to -60mV)
either positive charges exit or negative charges enter cytosol makes membrane potential more negative (change from -70 to -80 mV)
local potentials are sometimes called this, vary greatly in size, reversible
uniform, rapid depolarization and repolarization of membrane potential, only generated in trigger zones (axolemma, axon hillock, and initial segment of axon)
refers to an event (action potential) that either happens completely or does not occur at all
depolarization, repolarization, hyperpolarization
membrane potential rises towards zero, then becomes positive briefly
membrane potential returns to a negative value
membrane potential temporarily becomes more negative than resting membrane potential
action potentials must do this, along entire length of axon to serve as long-distance signaling service
down axon is nerve impulse
where neuron meets target cell (neuronal synapse if another neuron) can be electrical or chemical
occurs between cells electrically via gap junctions, in areas of brain responsible for programmed automatic behaviors (breathing), in cardiac and visceral smooth muscle to allow for coordinate muscle activity
make up the majority of synapses in the nervous system, more efficient than electrical synapses, convert electrical signals into chemical signals, and no signal strength is lost (as at electrical synapses)
each neuron has only one axon (nerve fiber) can generate and conduct action potentials
where axon originates
branches extending from main axon
small branches arising from axon
arise from telodendria, components that communicate with a target cell
plasma membrane surrounding axon and its cytoplasm (axoplasm)
single axon and multiple dendrites, over 99% of all neurons
one axon and one dendrite and cell body between them, eye and olfactory epithelium (nasal cavity)
only one fused axon, extends from cell body, divides into 2 processes, one carriers sensory information from sensory receptors to cell body, other carriers sensory information from cell body to spinal cord
carry into toward CNS, neuron cell bodies in PNS receive info from sensory receptors and relay information via axons to brain or spinal cord, usually pseudounipolar or bipolar
relay info within CNS between sensory and motor neurons, most neurons in body, multipolar, communicates with many other neurons
carry info away from cell body in CNS to muscles and glands, mostly multipolar
provide structural support and protection for neurons also maintain their environment, able to divide and fill in space left behind when neuron dies
astrocytes, oligodendrocytes, microglia, ependymal cells
Schwann cells, Satellite cells
large star-shaped cells, many processes terminating in end-feet, functions include: anchor neurons and blood vessels in place, transport of nutrients and gases between blood vessels and neurons, formation of blood-brain barrier, repair damaged brain tissue by rapid cell division
also in CNS, radiating processes with flattened sacs, wrap around axons of nearby neurons to form myelin
small, scarce cells, activated by injury into wandering phagocytic cells within CNS, ingest disease-causing microorganisms, dead neurons, and cellular debris
ciliated cells, line hollow spaces within CNS, manufacture and circulate cerebrospinal fluid
encircle axons in PNS to provide them with myleination
surround cell bodies of neurons in PNS, provide supportive functions
layers of the plasma membrane of Schwann cell or oligodendrocyte in PNS and CNS respectively
neuroglial cells wrap multiple layers of membrane (myelin) around axon, insulates axon (prevents ion movements), increases speed
segments of axon covered by neuroglia
gap between adjacent neuroglia, where myelin sheath is absent
composed of myelinated axons, appear white
composed of neuron cell bodies, unmyelinated dendrites and axons, appear gray